Underbed thread trimming mechanism for sewing machines

ABSTRACT

An underbed thread trimmer for both the needle and bobbin threads of a lockstitch sewing machine is disclosed in which a thread pick-up finger is moved across the path of the threads to be severed, and in which during return of the thread pick-up finger a cam associated therewith effects the opening and closing of a scissor type thread cutter.

e United States Patent [1 1 n 11 3,709,176. Papajewski et al. 1 Jan. 9, 1973 [541 UNDERBED THREAD TRIMMING mnn et al. i

' arris MECHANISM FOR SEWING 3,308,776 3/1967 lva'nko et al. l 12/252 X MACHINES 7 9,4 ,105 8/1969 Aoyama ..112/252' [75] Inventors: Reinhold Papajewski, 7501 Buchig; 5 3 M970 fia f "112/252 Erich Gmessen 75 Karlsruhe Dur 3,6Q 2,l70 8/1971 Sakashlta "112/25 2 lach both of Grmany 3,648,634 3/1972 Van Hazendonk ..1 12/252 [73] Assignee: The Singer Company, New York, P' Examiner-Werner Schroeder Attorney-Marshall J. Breen [22] Filed: Oct. 8, 1971 [57] ABSTRACT [21] App]? 187710 An underbed thread trimmer for both the needle and bobbin threads of a lockstitch sewing machine is dis- [52] U.S.Cl ..l12/252 closed in which a thread pick-up finger is moved [51] Int. Cl. ......'.....D05b 65/00 W088 the P of the threads to be severed, and in [58] Field 6: Search ..112/252 which during of the thread P k-up finger cam associated therewith effects the opening and closing of [56] References Cited a scissor type thread cutter.

UNITED STATES PATENTS 5 Claims,-9 Drawing Figures 2,474,710 6/1949 Wood i; ..112/2s2 9| 7.. A lob Q 99 90 a V 7 [0,52% '2' I22 z% P lol 2 42 Q HOIOG I 6 @7731; 6 i k 6 2 v @T so E: I09

47 40 I4 33 32 0 l3! :5 i

m- :11 I 0 W PATENTEDJAH' 9 1915 3.709 1 76 sum 1 or 2 INVENTQR. Reinhold POPCIjGWSkI Erich Gillessen WITNESSI q Y M 0 //Z M (M 1.. ATTORNEY PATENTEDJAN 9197s 3.709.176

SHEET 2 [1F 2 INVENTQR. Rejnhold POPOJGWSKI BY El'lCh Glllessen WITNESS: v 4Q 4m MZ ATTORNEY UNDERBED THREAD TRIMMING MECHANISM FOR SEWING MACHINES BACKGROUND OF THE INVENTION Sewing machine thread trimming mechanisms'are known in which a thread pick-up finger carries the" threads to a thread cutting device. In one previously known form, the thread cutting device must be actuated separately from the thread pick-up finger so that SUMMARY OF THE INVENTION This invention provides an underbed thread trimming mechanism for a lockstitch sewing machine in which both the thread pick-up finger and a thread cutting device are operated by a single actuator thus DESCRIPTION OF THE DRAWINGS With the above and additional objects and advantages in view as will hereinafter appear, this invention will be described hereinbelow with reference to a preferred form of construction illustrated in the accompanying drawings in which:

FIG. 1 is a bottom plan view ofa sewing machine bed having the underbed thread trimmer of this invention applied thereto,

FIG. 2 is a cross sectional view of a portion of the mechanism in the sewing machine bedof FIG. 1 particularly in the vicinity of the loop taker taken substan- I tially along line 22 of FIG. 1 and including the sewing threads in readiness to be cut,

FIG. 3 is a cross-sectional view taken substantially along line 3-3 of FIG. 1 showing the thread pick-up finger extended between the bobbin thread and the path of needle reciprocation,

FIG. 4 is a cross-sectional view taken substantially along line 4-4 of FIG. 1 showing another portion of the mechanism in the sewing machine bed of FIG. I particularly in the vicinity of the cam means for actuating the thread trimming mechanism also with the machine frame broken away,

FIG. 5 is a perspective view of the cam means for actuating the thread trimming mechanism, and

FIGS. 6, 7, 8, and 9 are bottom plan views of the thread trimmer assembly partially broken away to illustrate the details of the mechanism and showing different positions of the parts in which:

FIG. 6 illustrates the thread pick-up finger during movement to the left toward the sewing threads,

FIG. 7 illustrates the thread pick-up finger in fully extended position and includes a fragment of the sewing machine throat plate,

FIG. 8 illustrates the thread pick-up finger partially retracted with the cam means forcing the scissor type thread cutter into an open position, and 1 FIG. 9 illustrates the thread pick-up finger in fully retracted position and with the thread cutter closed.

7 Referring to the drawings, the underbed thread trimming mechanism of this invention is illustrated as applied to the Class 4576 lockstitch zigzag sewing machine manufactured by The Singer Company. Only the work supporting bed 1 l of the sewing machine is illustrated in the accompanying drawings, since the remaining portions of the sewing machine do not form a direct part of this invention and may be of any wellknown construction. The portions of the sewing machine frame which have not been illustrated support an eye-pointed thread carrying needle 12 which is reciprocated endwise through a needle aperture 13 ha throat plate 14 carried on the bed 11. Also supported adjacent to the needle is a presser member 15 which holds a work fabric W against the throat plate 14. The needle 12 cooperates in the formation of lockstitches with a loop taker 16 journalled beneath the bed 11. Preferably, the loop taker is carried on a shaft 17 journalled in a gear box 18 into which projects a bed shaft 19 for driving the loop taker. The bed shaft may be driven by a timing belt 20 preferably at the rate of one revolution for-each reciprocation of the needle, with gearing (not shown) in the gear box 18 serving to rotate the loop taker two revolutions for each reciprocation of the needle. The loop taker is arranged on an axis which extends transversely across the bed 11 and the needle aperture 13 in the throat plate is elongated lengthwise of the bed 11 in order that the needle 12 may be jogged from side to side to form zigzag stitches.

As illustrated in FIG. 2 a bobbin 25 on which is wound a supply of bobbin thread B is journalled in the loop taker and extends from the bobbin upwardly through the needle aperture 13 to the work W during sewing. Keeping in mind that the loop taker 16 rotates in a counterclockwise direction as viewed in FIG. 2, loops of needle thread will be seized by a loop seizing beak 26 on the loop takerand initially drawn to the left as shown at N in FIG. 2, following which on a continued rotation of the, loop' taker, the'seized needle thread loops are passed about the bobbin 2'5 and cast from the loop taker in a position on the right hand side as viewed in FIG. 2 and is indicated at N, from which position the needle thread loops are drawn upwardly and set into the work W.

The bed shaft 19, also carries afeed advance drive element 30 and a feed lift crank 31 which cooperates in a well-known fashion to impart work feeding movement to a material feed bar 32 to which a feed dog 33 is secured. The feed dog 33 operates through slots 34 in the'throat plate 14 as is well known in the art.

For severing both the bobbin thread B and the needle thread N at the conclusion of a line of stitches, the present invention provides a thread trimming sor type thread trimming device which is also carried beneath the slide plate as will be described in detail hereinbelow. This invention also includes, as will be described in detail below, a drive mechanism for the thread trimmerwhich is actuated from the bed shaft 19.

Referring to FIGS. 6 through 9, the slide plate 40 is formed with spaced downturned ears 42 between which extends a guide rod 43. Slidably embracing the guide rod 43 are the upturned limbs 44 of a bracket 45 which is also slidably constrained in a track groove 46 which is formed along an edge of a gib 47 which is secured by fastening screws 48 against a block 49 depending from the slide plate 40. Journalled for limited turning movement in the bracket 45 is a pivot pin 50 fixed on a carrier 51 to which is secured a thread pick up arm 52 formed on the free extremity with a threadengaging hook 53. A stud 54 which is-secured to the pick-up arm carrier 51 projects through the clearance opening 55 in the bracket 45. The stud 54 serves as the connection element to which is secured the means for driving the pick-up arm back and forth. The clearance opening 55 provides for limited movement of the stud therein and a consequent limited turning movement of the pick-up arm in addition to the major translatory movement of the pick-up arm parallel to the guide rod 43. Also pivotally supported on the pivot pin 50 is an adjusting plate 56 which is formed with a clearance opening 57 embracing the stud 54 and with an elongate slot 58 accommodating a clamp screw 59 threaded into the'bracket 45. By adjusting the angular position of the adjusting plate 56, the position of the clearance opening 57 embracing the stud 54 may be changed thus providing an adjustable stop determining the extreme position of the pick-up arm 52 relatively to the guide rod 43.

Carried beneath the slide plate 40 in a fixed position thereon by fastening screws is a ledger blade 71 formed with a cutting edge 72. The ledger blade cooperates in severing thread with a pivoted knife blade 73 formed with a thread-cutting edge 74. The knife blade 73 is journalled on a shouldered pivot screw 75 threaded in the slide plate 40. The pivoted knife blade 73 if formed with a radial arm 76 to which is fastened a tension spring 77 anchored on one of the downturned ears 42 beneath the slide plate. The tension spring 77 serves to bias the knife blade 73 into closed position in which the cutting edges 72, 74 overlap. The knife blade 73 is also formed with a cam lobe 78 by which, as will be described below, the scissor type thread trimmer can be driven upon.

Carried on a pivot pin 80 in the bracket 45 is an L" shaped camming lever 81 having one limb 82 disposed adjacent to the block 49 beneath the slide plate 40 and another limb 83 extending co-planar with and against the cam lobe 78 of the knife blade 73. A light coil spring 84 biases the camming lever 81 in a clockwise direction as viewed in FIGS. 6 through 9 so as to urge the limb 82 of the lever always toward the block 49.

The camming lever 81 will thus be moved backand forth relatively to the cam lobe 78 as the bracket 45 is moved back and forth along the guide rod 43. When the camming lever 81 is moved toward the right past the cam lobe 78 as shown in FIG. 6, the camming lever 81 can be turned in a counterclockwise direction about the pivot pin 80 causing the limb 82 of the camming lever to be moved out of contact with the block 49. When the camming lever 81 is moved toward .the' left, however, the camming lever cannot be turned, but instead will shift the cam lobe 78 as shown in FIG. 8 causing the scissor type thread-cutting blades-71, 73 to shift into an open position. When the bracket 45 is shifted completely to the left as viewed in FIG. 9, the cam lever arm 83 will be shifted beyond the cam lobe 78 thus releasing the knife blade 73 to be moved into the closed thread-cutting position by the tension spring 77.

For actuating the thread pick-up arm 52 in its back and forth movement, a lever is supported on a fulcrurn .pin 91 fixed in the sewing machine bed llxThe fulcrum pin 91 may be carried conveniently in a bottom cover 92which closes the gear box 18. The lever 90 is formed with an arm 93 which extends on one side of the stud 54 attached to the pick-up arm carrier 5l.

One arm ofa coil spring 94 which encircles the fulcrum bottom cover biases the stud 54 against the lever arm 93. Because of the spring 94, the lever 90 will drive the pickup arm 52 positively in a direction toward the left as viewed in FIG. 1 but indirectly and with the capacity for yielding in a direction to the right as viewed in FIG. 1. By means of a pivotal connection 95 to another arm 96 of the lever 90, a drive link 97 is connected thereto. At the opposite extremity the drive link97 is formed with a shoulder 98 against which an operating lever 99 is constrained by a nut 100 which is threaded on the extremity of the drive link. The operating lever 99 is pivoted on a fulcrum pin 101 secured in a bracket 102 which is fixed by the screws 103 beneath the sewing machine bed. The operating lever 99 at the extremity opposite the drive link 97 is formed with a cam follower projection 104 which is adapted to track an axial cam surface indicated generally at 105 formed on a cam element 106. As best illustrated in FIG. 5 the cam element 106 is formed with a 'slot 107 which snugly embraces the bed shaft 19 and set screws 108 serve to secure the cam element 106 fast on the shaft 19. The slot 107 permits the cam element to be positioned on and removed from the shaft 19 conveniently.

The cam surface 105 is preferably formed with three operating levels. A first level 109 permits the cam follower projection 104 of the operating lever 99 to move sufficiently to the right as viewed in- FIG. 1 so that the pick-up arm 52 .will be shifted into fully extended .position as shown in FIG. 7. An intermediate level 110 shifts the pick-up arm 52 into a partially retracted position as shown inFlG. 8 to cause the scissor type threadcutters to be moved into the open position and. to shift the pick-up arm so as to carry the threads seized thereby between the opened cutting edges 72, 74 of the cutter. An outer level 1 1 1 of the cam surface shifts the pick-up arm into an extreme left hand position as viewed in FIG. 9 in which the thread cutting blades are released for movement into overlapped thread cutting position. A light wire spring 1 15 is secured by a fastening screw 1 16 to the knife blade 73 and projects slightly beyond the cutting edge 74 of the knife blade so as to trap and confine the threads to be cut in a favorable position between the cutting edges 72, 74.

Pivoted on a pivot pin 120 on the bracket 102 is a latch lever 121 formed with a latch notch 122 engageable with a latch pin 123 on the operating lever 99. The latch lever 121 is biased by means of a spring 124 into the engaged position of the latch notch 122 with the latch pin 123 as illustrated in FIG. 1. In this spring biased position of the latch lever 121, the operating lever 99 will beheld by the latch out of engagement with the cam surface 105, and the underbed thread trimming mechanism will be restrained in a dormant condition. For releasing the operating lever 99 so that the underbed thread trimming mechanism may be operated, an electric solenoid 130 is secured by fastening screws 131 beneath the sewing machine bed 11 and an extension 132 of the solenoid armature is pivotally connected as at 133 to the latch lever 121.

The electric solenoid 130 may be energized momentarily to release the operating lever 99 and initiate a cycle of operation of the underbed thread trimmer by any known arrangement. Reference is made to the U.S. Pat. No. 3,386,402 June 4, 1968 to R. J. Ross which discloses an electric control circuit operable together with a needle positioning device which might also be used with the present invention. U.S. Pat. No. 3,386,402, which is incorporated herein by reference, includes a solenoid 2 for which the electrical control circuit may be connected to the present solenoid 130 to provide for the momentary actuation thereof.

In operation, the precise time at which the solenoid 130 is energized is not of a critical nature to the successful operation of this device. it is sufficient if the solenoid 130 be actuated while the cam follower projection 104 is opposite the lower level 109 of the cam surface 105 so that the pick-up arm 52 of the underbed thread trimmer will be shifted by the spring 94 into extended position as shown in FIGS. 3 and 7 during the last needle penetration of a sequence of stitch formation. The clamp screw 59 may be used to secure the adjusting plate 56 in a selected position so that the pickup arm 52 will be accurately located to move forwardly without striking the needle 12 and without deflecting the threads. On the return stroke, the pick-up arm 52 can swing slightly about the pivot pin 50 because of the clearance between the stud 54 and the opening 57. The hook 53 can thus swing laterally towards the threads to be seized. The thread engaging hook 5.3 on the pick-up arm 52 will thus move in a path in which it will grasp the final needle thread loop marked N on FIG. 2 as this needle thread loop is released from the loop taker. The cam element 106 will then regulate the operation of the underbed thread trimmer in timed relation with the operation of the machine needle and loop taker so that the thread pick-up arm 52 will be gradually shifted into partially retracted position by the intermediate lever 110 of the cam element 106 only after both the needle thread loop N and the bobbin thread B will have been seized by the pick-up arm 52. The thread engaging hook 53 on the pick-up arm 52 will then carry the bobbin thread B and the needle thread N into a position between the thread-cutter edges 72, 74.

The outer level 111 of the cam surface 'preferably is timed so as to influence the operating lever 99 to cause the closing of the scissor type thread cutter only when the needle has reached an extreme upward position and severing of the the needle has reached an extreme upward position and severing of the threads is desired. The motion of the pick-up arm 52 from extended to reciprocated position in response to the cam surface 105 is therefore, completely independent of the motion of the knife blade 73 which closes because of the tension spring 77. The motions of the thread pick-up arm 52 and of the knife blade 73, therefore, may each be selected separately with regard to the specific operating conditions which are deemed to be best for each individual mechanism.

By providing for operation of the thread-cutting knife as a result of the final movement of the thread pick-up arm, only one actuating mechanism is required, namely that for shifting the thread pick-up arm, and in addition to obviating the requirement for a separate actuator for the thread-cutting knife, the arrangement results in which the timing of the threadcutter operation is advantageously correlated with the operation of the thread pick-up arm.

Having set forth the nature of this invention, what is claimed herein is:

1. An underbed thread trimmer for a sewing machine comprising a thread pick-up arm formed with a thread catching hook, means shiftably supporting said thread pick-up arm for movement alternately from a retracted position into an extended position in which said thread catching hook'is moved into position for engagement with the sewing threads to be trimmed and return into the retracted position, a scissor type thread severing device including a pair of cooperating thread severing blades arranged contiguous to the path of said thread catching hook, means supporting said thread severing blades for relative movement into an open position or into an overlapping thread severing positionQmeans biasing said thread severing blades into overlapping thread severing position, and interengaging cam means associated with said thread severing device and with said thread pick-up arm effective during the return movement of said thread pick-up arm for in seriatim opening and then releasing said thread severing blades for movement by said biasing means into overlapping thread severing position.

2. An underbed thread trimmer for a sewing machine I as set forth in claim 1 in which said thread pick-up arm and said scissor type thread severing device are carried on a single bracket adapted to be secured to a sewing machine.

3. An underbed thread trimmer for a sewing machine as set forth in claim 1 in which said interengaging cam means includes a spring loaded pawl member arranged so as to render said cam means ineffective during movement of said thread pick-up arm toward said extended position.

4. in a lockstitch sewing machine having a work supporting bed, a thread carrying needle cooperating in the formation of stitches with a loop taker which is arranged beneath the bed and houses a thread carrying bobbin, and drive means for operating said needle and loop taker in timed relation, an underbed thread trimmer comprising a thread pick-up arm formed with a thread catching hook, means shiftably supporting said thread pick-up arm for movement alternately from a retracted position into an extended position in which said thread catching hook is moved into position for engagement with the sewing threads to be trimmed and return into the retracted position, a scissor type thread severing device including a pair of cooperating thread severing blades arranged contiguous to the path of said thread catching hook, means supporting said thread severing blades for relative movement into an open position or into an overlapping thread severing position, means biasing said thread severing blades into overlapping thread severing position, and interengaging cam means associated with said thread severing severing blades for movement by said biasing means into overlapping thread severing .position, operating linkage connecting said thread pick-up arm with a cam follower, and cam means cooperating with said cam follower and driven by said drive means for said needle and loop taker for actuating said thread trimmer in a timed relation to the operation of said needle and loop taker.

5. The combination as set forth in claim 4 in which spring means is provided for biasing said thread pick-up arm toward said extended position,- and in which said operating linkage for said thread pick-up arm includes a separable connection rendering said linkage effective only to shift said thread pick-up arm positively toward the retracted position. 

1. An underbed thread trimmer for a sewing machine comprising a thread pick-up arm formed with a thread catching hook, means shiftably supporting said thread pick-up arm for movement alternately from a retracted position into an extended position in which said thread catching hook is moved into position for engagement with the sewing threads to be trimmed and return into the retracted position, a scissor type thread severing device including a pair of cooperating thread severing blades arranged contiguous to the path of said thread catching hook, means supporting said thread severing blades for relative movement into an open position or into an overlapping thread severing position, means biasing said thread severing blades into overlapping thread severing position, and interengaging cam means associated with said thread severing device and with said thread pick-up arm effective during the return movement Of said thread pick-up arm for in seriatim opening and then releasing said thread severing blades for movement by said biasing means into overlapping thread severing position.
 2. An underbed thread trimmer for a sewing machine as set forth in claim 1 in which said thread pick-up arm and said scissor type thread severing device are carried on a single bracket adapted to be secured to a sewing machine.
 3. An underbed thread trimmer for a sewing machine as set forth in claim 1 in which said interengaging cam means includes a spring loaded pawl member arranged so as to render said cam means ineffective during movement of said thread pick-up arm toward said extended position.
 4. In a lockstitch sewing machine having a work supporting bed, a thread carrying needle cooperating in the formation of stitches with a loop taker which is arranged beneath the bed and houses a thread carrying bobbin, and drive means for operating said needle and loop taker in timed relation, an underbed thread trimmer comprising a thread pick-up arm formed with a thread catching hook, means shiftably supporting said thread pick-up arm for movement alternately from a retracted position into an extended position in which said thread catching hook is moved into position for engagement with the sewing threads to be trimmed and return into the retracted position, a scissor type thread severing device including a pair of cooperating thread severing blades arranged contiguous to the path of said thread catching hook, means supporting said thread severing blades for relative movement into an open position or into an overlapping thread severing position, means biasing said thread severing blades into overlapping thread severing position, and interengaging cam means associated with said thread severing device and with said thread pick-up arm effective during the return movement of said thread pick-up arm for in seriatim opening and then releasing said thread severing blades for movement by said biasing means into overlapping thread severing position, operating linkage connecting said thread pick-up arm with a cam follower, and cam means cooperating with said cam follower and driven by said drive means for said needle and loop taker for actuating said thread trimmer in a timed relation to the operation of said needle and loop taker.
 5. The combination as set forth in claim 4 in which spring means is provided for biasing said thread pick-up arm toward said extended position, and in which said operating linkage for said thread pick-up arm includes a separable connection rendering said linkage effective only to shift said thread pick-up arm positively toward the retracted position. 